The present invention relates to an optical pickup device and an optical disc apparatus.
As a background art of this technical field, for example, there is JP-A-2006-344344 which describes an object “to precisely obtain desired signals from an optical disk having a plurality of recording layers”, and discloses a solution as follows: “an optical beam of P-polarized light emitted from a light source unit 51 is reflected by an optical disc 15 and becomes S-polarized light to enter a lens 61. Then, both of quarter wave plates 62 and 63 impart an optical phase difference of a +quarter wavelength to the optical beam having entered an +X side of an optical axis, and impart an optical phase difference of a −quarter wavelength to the optical beam having entered the −X side. Thus, signal light through the quarter wave plate 63 becomes S-polarized light, and stray light becomes P-polarized light, so that a polarization optical element 64 transmits only the signal light.”
Further, in JP-A-2009-170060, there is described “it is an object to provide an optical pickup device capable of providing stable servo signals by preventing the influence of stray light from other layers on a focusing error signal and tracking error signal during recording and reproducing operations in a multilayer optical disc.” A solution is disclosed as follows: “reflected light from the multilayer optical disc is divided into a plurality of regions, divided luminous fluxes are focused on different positions of a photodetector, the focusing error signal is detected by a knife edge method using a plurality of the divided luminous fluxes, and the tracking error signal is detected by using the plurality of divided luminous fluxes”. Further, “when a focus is on an intended layer, the divided region of a luminous flux and a light receiving surface are arranged so as to prevent incidence of stray light from the other layers to a light receiving surface for the servo signal of the photodetector.”